The Roar Beneath the Waves

The sound level below sea level isn’t what you might expect.

Published January 05, 2015

On the surface, the vast expanse of ocean may seem calm and tranquil—an oasis from the perpetual buzz of human activity on land. But below the façade of gentle waves and rippling tides lies a cacophony of sound, an unrelenting whirring occasionally perforated by a barrage of shrill whistles. Anthropogenic, or man-made, noise has infiltrated this underwater world, leaving its inhabitants with the clamorous consequences of commercial shipping, oil and gas exploration, construction and military sonar.

Aquatic animals have evolved over time to survive the ocean’s dark depths through an acute sensitivity to sound. Their ability to hunt, navigate and communicate depends on their capacity to hear. An inability to do so can prompt them to vacate their habitats, possibly abandoning a rich food source in the process; worse, it could lead to accidental collisions with ships due to a failure to distinguish mechanical sounds from natural ones.

Sixty years ago, this wasn’t an issue. The loudest noises entering their environment originated from waves, wind, precipitation, ice movement and fish. But the world has become a noisier place since then. In fact, anthropogenic noise has doubled every decade for the past 50 years.

Common Culprits

Industrial shipping undoubtedly played a role in this surge of sound. Between 1980 and 2009, the global merchant fleet nearly doubled in size, steadily amplifying the commotion caused by the engines, propellers, generators and bearings driving these cargo ships. This ship noise unfortunately occupies the same frequencies many whale species use to communicate.

The effect of this overlap is being seen in Cape Cod Bay, where it’s directly impacting the way right whales interact with each other. Research indicates the “acoustic bubble” of right whales in this area—meaning the distance over which whale calls can travel and be heard—has shrunk by 80 percent. To compensate, these endangered mammals have begun “shouting” over the din, significantly increasing the volume and frequency of their calls.

In other places of the world, seismic survey operations are adding their own disturbances to the mix. Oil companies search the seafloor for oil and natural gas using airgun arrays, which fire ear-splitting sound pulses through the ocean’s depths. Blasted every 10 to 60 seconds for days or months at a time, it’s enough to send whales fleeing their feeding grounds.

Navy Noise

But perhaps the most powerful and controversial form of noise pollution resonates from the governmental body protecting another species of mammal: us. The U.S. Navy has come under fire in the past two decades for its use of sonar, which it has employed since the Cold War to detect enemy submarines over great distances. In the same way bats use echolocation, these sonar systems transmit sound waves hundreds of miles through the water to reveal any potential threats to national security.

In the process, they also deliver an auditory assault on aquatic animals in their path. Decades of research—much of it by the U.S. Navy itself—has confirmed a link between naval sonar and mass strandings of whales. Examinations of these animals have revealed brain and inner-ear hemorrhaging, symptoms found in severe cases of decompression sickness. Also known as “the bends,” this condition can be deadly to scuba divers who rise to the water’s surface too quickly. Scientists theorize the blasts cause whales to dive too deeply or surface too rapidly in a desperate attempt to escape the noise.

Any Sound Solutions?

Although the Navy has spent millions of dollars researching the effects of sonar on marine mammals, it’s unlikely it will stop using this tactic anytime soon. The issue was actually taken to the Supreme Court in 2008, and the majority agreed that the concern of military preparedness outweighed the potential environmental repercussions.

However, environmentalists have had some success in mitigating the problem. “The Navy has now agreed to conduct environmental impact statements for all sonar exercises on its U.S. coastal ranges, which is much more than they did in the 1990s,” says “War of the Whales” author Joshua Horwitz.

The International Fund for Animal Welfare also states in a 2013 report that “the Navy is studying frequency response issues in whales, particularly beaked whales, presumably with an eye toward finding a less dangerous frequency to transmit at.”

Unfortunately, none of the sources of noise pollution are going to simply cease. As long as there’s a demand for oil, companies will conduct seismic surveys. And until we develop one of those teleportation devices promised in futuristic films, commercial shipping will continue.

To realistically protect aquatic animals in the world we’ve created, conservationists are pushing for the establishment of more national marine sanctuaries. These sites provide a safe haven for critical ocean habitats, such as whale feeding and breeding grounds. Research also offers hope, laying the groundwork for new technologies that could reduce the problem in the future.

Until then, it’s up to individuals to promote awareness of this oceanic issue and encourage policy-makers to keep the noise level to a minimum so the world can find ways to better share our seas.